Letter | Published:

Exchange Equilibria of Sodium on Some British Soils

Nature volume 212, page 548 (29 October 1966) | Download Citation

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Abstract

BECKETT1,2 has discussed potassium–calcium exchange energies in soil suspensions, using a development of a thermodynamic approach suggested by Woodruff3 and Schofield and Taylor4. He showed that a graph of the “activity ratio” (called ARK) in the solution plotted against the changes in exchangeable soil potassium (ΔK) is usually linear except at small values of ARK where it curves sharply and becomes asymptotic to the ΔK axis (Fig. 2). ARK is directly related to the change in free energy when equivalent amounts of potassium and calcium are exchanged between the soil and solution phases. Beckett2 considers that the curvature is produced by a small proportion of potassium ions held on discrete exchange sites with a greater preference for potassium relative to calcium. These sites determine the exchange energy when nearly all the exchangeable potassium is removed. Very recently he has found evidence of similar behaviour for calcium and magnesium5.

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References

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Author information

Author notes

    • P. B. H. TINKER

    Present address: Department of Agriculture, University of Oxford.

Affiliations

  1. Brooms Barn Experimental Station, Higham, Bury St. Edmunds, Suffolk.

    • P. B. H. TINKER
  2. Rothamsted Experimental Station, Harpenden, Hertfordshire.

    • J. BOLTON

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DOI

https://doi.org/10.1038/212548a0

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